AL HUDAYDAH, Yemen — A pharmacist, a delivery man driving a motorcycle and a fishmonger. After an eruption of what aid groups have described as indiscriminate violence against civilians in Yemen’s crucial Red Sea port city, one basic fact is clear: 55 people are dead and 170 others wounded.

Yet like so much of Yemen’s civil war, many elements of the multiple attacks on Thursday remain hazy: who was responsible, and who or what was the intended target. The main combatants in the battle for Al Hudaydah, a city of 600,000 people, have blamed each other for explosions in a residential neighborhood, at the city’s fish market, and outside the main hospital.

The Houthi rebels controlling Al Hudaydah, the country’s vital lifeline for food and medicine, and medics treating the wounded say the Saudi-led coalition launched airstrikes against civilian targets. The Saudis blamed the Houthis, pointing to evidence compiled over the weekend suggesting that mortars, which are launched from the ground, were used rather than missiles from planes.

So far, neither international aid groups nor the United Nations has attributed blame. Instead, they have condemned the attacks as the latest in a litany of assaults, during more than three years of conflict, that appear to violate international laws of warfare.

The United Nations classifies Yemen as the world’s worst humanitarian crisis. Two-thirds of the nation’s 29 million people rely on international aid, and Al Hudaydah is the point of entry for 70 percent of that aid.

Tens of thousands of people have been killed in fighting and acute medical crises exacerbated by the civil war, which started in 2015 after power-sharing negotiations broke down.

The nation is currently divided into competing spheres of influence, with the Houthis, a mostly Shiite group, in control of their ancestral homeland in the northwest; Al Hudaydah; and the capital, Sana. The militaries of Saudi Arabia and the United Arab Emirates, which describe the Houthis as Iranian proxies, support, arm and train opposing local militias, in hopes of restoring to power the controversial but internationally recognized president, Abdu Rabbu Mansour Hadi.

In June, the Saudi-led coalition launched the battle for Al Hudaydah in an effort to tip the power balance against the Houthis, ignoring a diplomatic outcry over concern for the safety of the city’s residents and the threat that fighting could pose to humanitarian supply lines.

Since then, residents have become accustomed to the buzzing of coalition fighter jets, which make frequent bombing raids on the outskirts of the city, and the roar of infantry battles. Fighting over the weekend between Emirati-backed Yemeni forces and Houthis on the city’s southern suburbs killed dozens of fighters, The Associated Press reported.

The attacks have destroyed much of the systems that deliver fresh water to the city and dispose of its wastewater, aid groups said.

But the fight for Al Hudaydah has not produced the mass civilian casualties that were feared. The Arab coalition has decided it has neither the skill nor the fortitude for a bloody, heavily contested urban battle, according to a senior coalition official and an American official.

The violence on Thursday, however, revived those concerns.

“These attacks literally came out of the blue,” said Jolien Veldwijk, the assistant country director for CARE, an aid group. “We keep thinking that it cannot get any worse. But unfortunately we are wrong.”

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Yemeni government forces preparing to fight Houthi rebels near Al Hudaydah last month. The city is a vital lifeline for humanitarian aid.CreditNajeeb Almahboobi/EPA, via Shutterstock

Through lunchtime on Thursday, numerous bombs fell on a neighborhood next to a Houthi military compound. A resident whose house was damaged said that there were no casualties, and that other neighbors had said the security compound was mostly abandoned at the time of the attack.

Around 4 p.m., three bombs hit the city’s main fish market in quick succession. About 30 minutes later, two more detonated nearby, at the entrance to the central hospital, and a third struck the roof of the hospital records room, witnesses said.

Initial reports by medics and aid organizations indicated that fighter jets belonging to the Saudi-led coalition carried out the attack. The Saudis and Emiratis vigorously contested those allegations, telling reporters that their planned air operations for that day were targeting areas outside the city.

Fragments of munitions gathered at the attack sites as well as interviews with six residents and witnesses suggested that the weapons used on Thursday were mortars, not missiles, indicating that the attacks were launched from the ground.

The provenance of the mortars is unclear. Fragments recovered at the scene did not show manufacturers’ information or serial numbers that might indicate which arsenal the weapons came from.

Saudi and Emirati officials blamed the Houthis for the attack, saying that only the rebels were within mortar range of the places that were hit.

The Houthis continued to hold the coalition responsible.

Over the weekend, Houthi, Emirati and Saudi officials agreed to meet the United Nations special representative for Yemen in Switzerland in September to discuss a cease-fire and the possibility of restarting power-sharing talks.